Experts warn pot's health dangers are many and varied

From movies like Reefer Madness to Pineapple Express, the health effects of marijuana have been both minimized and exaggerated over the years. Many legalization advocates provide anecdotal evidence of high-achieving professionals who were life-time marijuana smokers, maintaining that marijuana ranks low on the vice-meter. Here is what the latest research reveals:

The active ingredient in marijuana, THC, affects the nerve cells in the part of the brain where memories are formed.

It can also seriously affect your sense of timing and coordination, making driving, household chores, physical labor or other activities dangerous. In 2005, nearly a quarter of a million people were admitted to emergency rooms for marijuana-related problems.

Marijuana smoke deposits four times more tar in the lungs and contains 50 to 70 percent more cancer-causing substances than tobacco smoke. Five joints a day equates to smoking 20 cigarettes a day. This can lead to chronic coughing, chest colds, bronchitis, lung infections, breathing problems and cancer of the head, neck, lungs and respiratory tract.

Marijuana limits your body’s ability to fight off infection.

Heavy use has been linked to depression, anxiety, and personality disturbances.

Marijuana can also be a malevolent mystery package, laced with substances such as PCP, formaldehyde and codeine cough syrup without your knowledge.

Marijuana can be addictive. In 2006, nearly 290,000 people entered drug treatment programs to kick a marijuana habit. It has not been proven that marijuana use leads to the use of other drugs, but many people who used marijuana before the age of 17 were more likely to use other drugs and develop addiction problems later on.